Portable communication terminals such as portable telephones and PDAs have become widespread recently, and they are changing so that they can be used for videophones, receiving content delivery services, or other multimedia communication. However, since there are limitations on the terminal capability and transmission capability of a portable communication terminal, there are limits to the functionality in multimedia communication, such as the screen size and the frame rate. When there is, around a user, a multimedia terminal that can perform more functional multimedia communication than a portable communication terminal can, it is desired to switch multimedia communication in which the portable communication terminal has been used as an end communication terminal to the highly functional multimedia communication terminal. For example, a user on a videophone using a portable communication terminal arrives at the user's home, and enters an environment where there is, around the user, a videophone terminal which is a multimedia communication terminal more functional than the portable communication terminal. At this time when the user arrives at the user's home, the user switches the multimedia communication from the portable communication terminal to the videophone terminal. This increases the screen size and frame rate and allows the user to do multimedia communication with a larger screen and higher picture quality.
Such switching of an end communication terminal in multimedia communication has been realized, for example, by transferring multimedia communication from one terminal to another. This technique is described, for example, in IETF RFC3261 and RFC3515. As for the start of control and change process in communication, a technique would be used which is described in ITU-T H.323, H.245, and Q.931, or in Japanese Patent Laid-Open Application No. 2000-115253, for example.